The present invention relates to a pneumatic impact damping device for a drill column, and, in particular, to an impact damping device used with a deep-hole hammer drill to divert the impacts and vibrations of the drill from the rotating machine rotating the drill column and from other parts of the drilling equipment.
U.S. Pat. No. 5,355,966 describes a drilling means with a deep-hole hammer drill at an inner drill column and a rotary percussion drill at an outer drill column. An impact damping device is provided that separates the impacts from the inner and the outer tube, respectively.
From German Patent 196 16 751, a device for superposed drilling is known wherein an outer column is connected with a head-piece onto which an percussion device may strike. Within the head-piece, a gas pressure reservoir is located having a hydraulic chamber in communication with a cylinder chamber. The hydraulic liquid In the cylinder chamber pushes forward a hydraulic piston to which the inner column is connected. The gas pressure reservoir separates the inner column, with the deep-hole hammer drill contained therein, from the impacts caused by the percussion device.
It is common with drill columns operated with a deep-hole hammer drill to arrange a pack of damping elements in front of the rotary drive, the elements keeping the deep-hole hammer drill impacts away from the rotary drive. The damping elements are rubber packages subjected to heavy wear.
A pneumatic impact damping device of the kind mentioned in the preamble of claim 1 is known from U.S. Pat. No. 4,055,338. This damping device comprises a cylinder chamber filled with gas, e.g. hydrogen, and sealed off by a piston. The piston is supported by a liquid buffer. Upon an axial movement of the cylinder, which is connected with a first portion of a drill column, the gas within the gas chamber is compressed thereby producing a spring and damping effect. This device has a gas chamber that is always closed, and it also has a liquid chamber always closed. Thus, it requires a certain maintenance to ensure the required volumes of gas and liquid.
It is the object of the present invention to provide a pneumatic impact damping device that is of simple structure and is functionally reliable while having a long service life.